Squirrel-cage rotor

ABSTRACT

The invention relates to a squirrel-cage rotor for an asynchronous machine, said squirrel-cage rotor having at least one laminated rotor core that comprises a plurality of grooves and said squirrel-cage rotor having at least one rotor cage comprising electrically conductive rotor bars that are embedded in the grooves of the laminated rotor core in such a manner that the rotor bars comprise at their two end regions an overlap beyond the laminated rotor core, and said rotor cage comprising short-circuit rings that are attached at the end face to the laminated rotor core and comprise a plurality of slots that are arranged in the region of their outer periphery and the end regions of the rotor bars protrude into said slots. The short-circuit rings comprise in each case at least two metal composite discs that comprise at least a first metal disc and a second metal disc that is connected in a planar manner to said first metal disc and is embodied from a different material thereto. Adjacent metal composite discs are arranged at least in part in such a manner that the first metal discs are facing one another. The rotor bars are bonded to the first metal discs in the region of the slots.

The invention relates to a squirrel-cage rotor for an asynchronous machine, said squirrel-cage rotor having at least one laminated rotor core that comprises a plurality of grooves and said squirrel-cage rotor having at least one rotor cage comprising electrically conductive rotor bars that are embedded in the grooves of the laminated rotor core in such a manner that the rotor bars comprise at their two end regions an overlap beyond the laminated rotor core, and said rotor cage comprising short-circuit rings that are attached at the end face to the laminated rotor core and comprise a plurality of slots that are arranged in the region of their outer periphery and the end regions of the rotor bars protrude into said slots.

The fundamental construction of squirrel-cage rotors for asynchronous machines is generally known from the prior art. Various methods are known for producing the rotor cage. In some cases, the entire rotor cage is cast in one piece. As a deviation from this, embodiments are known where the rotor bars are produced from a semi-finished product and are embedded in the grooves of the laminated rotor core. The short-circuit rings are subsequently cast on. A further variant provides in contrast to this to produce the short-circuit rings from correspondingly formed metal sheets. The metal sheets must have good electrically conductive characteristics and must be connected in a reliable manner to the rotor bars. This connection is formed in many cases by means of a soldering process, such as for example can be found in the document DE 34 21 537 A1.

Furthermore, squirrel-cage rotors are known from DE 195 42 962 C1, wherein the short-circuit rings are constructed from copper metal sheets and steel metal sheets that are positioned in an alternating manner with respect to one another. As a consequence, the mechanical stability of the short-circuit rings is to be improved and the in-laid steel metal plates are to limit the extent to which the short-circuit ring can expand even in the case of higher rotational speeds. The steel metal sheets are soldered to the copper metal sheets and the conductor bars.

It is proposed in the document DE 697 34 839 T2 to produce the short-circuit rings of a cage rotor from a bimetal metal sheet, in particular a steel-copper metal sheet. Bimetal short-circuit rings that are produced in this manner are then positioned with their steel face towards with the laminated rotor core, so that subsequently the short-circuit ring can be welded to the laminated rotor core.

The object of the invention is to provide an improved squirrel-cage rotor for an asynchronous machine. The improvement relates to the construction of the short-circuit rings and their connection to the rotor bars.

The invention is characterized by means of the features of claim 1. The other related claims relate to advantageous embodiments and further developments of the invention.

The invention includes a squirrel-cage rotor for an asynchronous machine, said squirrel-cage rotor having at least one laminated rotor core and having at least one rotor cage comprising electrically conductive rotor bars and short-circuit rings. The laminated rotor core comprises a plurality of grooves. The grooves can be embodied as grooves that are open in the radial direction towards the exterior. The rotor bars are embedded in the grooves of the laminated rotor core in such a manner that they comprise at their two end regions an overlap beyond the laminated rotor core. Short-circuit rings that comprise a plurality of slots that are arranged in the region of their outer periphery are provided on the end faces of the laminated rotor core and the end regions of the rotor bars protrude into said slots. The slots can be embodied as through-going openings that are open in the radial direction towards the exterior or are closed. In accordance with the invention, the short-circuit rings comprise in each case at least two metal composite discs that for their part comprise at least one first metal disc and a second metal disc that is connected in a planar manner to said first metal disc and is embodied from a different material thereto. Adjacent metal composite discs are arranged at least in part in such a manner that first metal discs of these metal composite discs are facing one another. The rotor rods are bonded, preferably welded, to the first metal discs in the region of the slots.

The invention is based on the consideration that the short-circuit rings of the rotor cage comprise in each case a plurality of metal composite discs. The metal composite discs comprise at least two metal discs that are embodied from different materials and are connected one to the other in a planar and electrically conductive manner. The materials of the metal discs differ from one another with respect to their density, electrically conductive characteristics, strength characteristics and their costs. Consequently the metal composite discs offer, in contrast to mono-metal discs, more freedom with regard to optimizing the short-circuit rings with respect to the electrical conductance value, weight, strength and costs. The choice of the mutually combined materials and the thickness ratio of the individual metal discs plays an important role. The metal composite discs must be connected to the rotor bars at their end regions in an efficient electrically conductive manner. The connection must be reliable and must not fail during the entire serviceable life of the machine even under the influence of forces such as during the operation of rapidly rotating components. Therefore, the connection between the rotor bars and the metal composite discs is a bonded connection, by way of example by means of a soldering process or preferably by means of a welding process. Since it is difficult to bond different metal materials to each other, the technique used to connect the rotor bars and short-shirt rings is selected such that essentially only the metal disc of a metal composite disc whose material can be best connected to the material of the rotor bars is connected to the rotor bars. Within the scope of this invention, this metal disc is described as the ‘first metal disc’ whereas a metal disc that is embodied from a different material thereto is described as the ‘second metal disc’. The current is transferred from the rotor bars to a metal composite disc by way of the bonded connections initially to the first metal disc. The planar bond between the metal discs renders it possible to transport the current within the metal composite disc with a minimum amount of electrical resistance. In accordance with the invention, the metal composite discs of the short-circuit rings are arranged at least in part in such a manner that the first metal discs of adjacent metal composite discs are facing one another. As a consequence, first metal discs, which are embodied from an identical material, of adjacent metal composite discs are positioned directly next to one another. This is achieved in the case of metal composite discs that comprise two metal discs by virtue of the fact that adjacent metal composite discs are arranged in a mirror-inverted manner with respect to one another with regard to their disc arrangement. Alternatively, solutions using multi-layer metal composite discs are possible.

The particular advantage of this type of construction of short-circuit rings resides in the fact that two adjacent metal composite discs can be connected to a rotor bar by means of a single connection process, by way of example by means of a single welding procedure. Consequently, outlay and costs for connecting the short-circuit rings to the rotor bars can be almost halved. Furthermore, it is possible to produce a reliable connection between two adjacent metal composite discs without additional outlay. This improves the electrical conductivity of the short-circuit rings and increases the mechanical stability.

In a preferred embodiment of the invention, the rotor bars can be embodied at least in part from a material that can be easily welded to the material of the first metal discs. It is possible to produce particularly reliable connections by means of a welding process. Suitable connection methods are by way of example laser welding or electron beam welding. The two materials that are welded one to the other preferably have melt temperatures or rather melt regions that are close to one another and also similar thermally conductive characteristics. The difference in melt temperatures or rather weld regions is preferably a maximum 20 K.

In a particularly preferred embodiment of the invention, the rotor bars can be embodied at least in part from a material whose base material is identical to the base material of the first metal discs. The two materials that are to be welded one to the other can therefore be different alloys of the identical base material. The two alloys can in many cases be easily welded as a result of the identical base material. In particular, the conductivity and the strength of a material can be purposefully influenced by means of suitable alloying elements. It is thus possible by way of example to manufacture the rotor bars preferably from an alloy that has a particularly high strength, whereas an alloy that has particularly good conductivity characteristics is used for the first metal discs of the short-circuit rings.

In an advantageous embodiment of the invention, the metal discs that are embodied from a different material and are part of the metal composite disc are connected one to the other in a planar manner using a plating technique. The plating technique is a particularly suitable method of connecting different metal materials in a planar manner one to the other, said materials being available in a strip or sheet metal form. A particularly suitable method for this purpose is the laser roll plating technique. The plating method renders it possible to produce in a favorable manner semi-finished products that are embodied from metal composites, by way of example bimetal strips. Semi-finished goods of this type can be metal composite discs that have been produced by means of a suitable separating method, by way of example stamping or laser cutting, and that are required in order to construct a short-circuit rotor in accordance with the invention.

In the case of an advantageous embodiment of the invention, the first metal discs can comprise at least one bevel on their outer periphery. It is preferred that this bevel extends in the radial direction at least as far as the slots. A bevel of this type provides the first metal disc with a geometry that is favorable for connecting to the conductor bars. The bevel produces a type of circumferential groove by means of which it is possible to access the connection site between the first metal disc and the conductor bar. If a soldering process is used, the solder material can be introduced into the groove and thus directed to the connection site. If a welding process is used, energy can be introduced into the weld site by means of the groove by way of example using a flame or a laser beam or electron beam.

In an advantageous embodiment of the invention, the first metal discs, in other words the metal discs that are bonded to the conductor bars, can be embodied from aluminum or an aluminum alloy. It is accordingly advantageous if the conductor bars are embodied at least in part from aluminum or an aluminum alloy. As a result of their density and their relatively good electrically conductive characteristics, aluminum and aluminum alloys are preferred materials for conductor bars and short circuit rings of a cage rotor. In order in this advantageous embodiment to improve the electric conductance of the short-circuit rings, the second metal discs of the metal composite discs are preferably embodied from copper or a copper alloy. As a consequence, a favorable compromise between electric conductance and weight is achieved. In a particularly advantageous embodiment of the invention, the thickness s₁ of the first metal discs is at least 60% of the thickness s of the metal composite discs. The first metal discs are embodied from aluminum or an aluminum alloy. In comparison to other metal materials, aluminum is characterized by virtue of a very low density and a favorable price in relation to its volume. If at least 60% of the metal composite discs are embodied from aluminum or an aluminum alloy, then they are characterized by means of a low weight and low costs.

In the case of an alternative advantageous embodiment of the invention, the first metal discs, in other words the metal discs that are bonded to the conductor bars, are embodied from copper or a copper alloy. It is accordingly advantageous if the conductor bars are embodied at least in part from copper or a copper alloy. As a result of their high electrically conductive characteristics, copper and copper alloys are preferred materials for conductor bars and short-circuit rings of a squirrel cage rotor. In order in the case of this advantageous embodiment of the invention to reduce the weight and the costs of the short-circuit rings, the second metal discs of the metal composite discs can be embodied preferably in aluminum or an aluminum alloy. As a consequence, a favorable compromise is achieved between electric conductance, weight and cost.

The invention is further explained with reference to the following exemplary embodiments and with reference to the schematic drawings, in which:

FIG. 1 illustrates a sectional view of a squirrel-cage rotor,

FIG. 2 illustrates an enlarged view of the view in FIG. 1 in the region of the connection between the rotor bar and a short-circuit ring,

FIG. 3 illustrates an enlarged view of a further embodiment of a squirrel-cage rotor in accordance with the invention in the region of the connection between the rotor bar and a short-circuit ring.

Mutually corresponding parts are provided with the same reference numeral in all figures.

FIG. 1 illustrates a sectional view of a squirrel-cage rotor 1 in accordance with the invention. The squirrel-cage rotor 1 has an essentially cylindrical shape with an axis A and a centrally arranged bore hole 4 for receiving a shaft, not illustrated. Said squirrel-cage rotor comprises a laminated rotor core 11 that is constructed in a manner known per se from individual metal sheets. The laminated rotor core 11 comprises a plurality of grooves 12, two of which are visible in the sectional view. Furthermore, the squirrel-cage rotor 1 comprises a plurality of electrically conductive rotor bars 2, two of which are visible in the sectional view, and also two short-circuit rings 3. The rotor bars 2 and the short-circuit rings 3 together essentially form the squirrel cage. The rotor bars 2 are embedded in the grooves 12 of the laminated rotor core 11 in such a manner that they comprise at their two end regions 21 an overlap beyond the laminated rotor core 11. Generally, the rotor bars 2 are not arranged in parallel to the axis A of the cage rotor 1 but rather are arranged inclined by a defined angle of twist with respect to the axis A. However, for reasons of clarity, this feature is not shown in the schematic illustrate in FIG. 1. The rotor bars 2 are embodied in the illustrated exemplary embodiment as solid mono-metal bars. However, it is also possible to use bi-metal bars and/or hollow bars. The short-circuit rings 3 are attached to the end faces of the laminated rotor core 11. The short-circuit rings 3 comprise in the region of their outer periphery a plurality of slots 31. The number and position of the slots 31 are to be selected such that said slots can be brought into alignment with the grooves 12 of the laminated rotor core 11. The end regions 21 of the rotor bars 2 protrude into the slots 31 of the short-circuit rings 3.

In accordance with the invention, the short-circuit rings 3 comprise in each case four metal composite discs 32 that for their part comprise in each case a first metal disc 33 and a second metal disc 34 that is connected in a planar manner to said first metal disc and is embodied from a different material thereto. In each case, two adjacent metal composite discs 32 are arranged in such a manner that the first metal disc 33 or second metal disc 34 that are embodied from an identical material are facing one another. If you count for each of the two short-circuit rings 3 the metal composite discs 32 commencing at the front face of the laminated rotor core, then in each case the second and the fourth metal composite discs 32 are arranged in a mirror-inverted manner with respect to the first and third metal composite disc 32. As a consequence, in each case between the first and the second and also between the third and the fourth metal composite disc 32, the first metal discs 33 that are embodied from an identical material are facing one another. Likewise, in each case between the second and the third metal composite disc 32, the second metal discs 34 that are embodied from an identical material are facing one another. In the schematic illustration of FIG. 1, adjacent metal composite discs 32 are illustrated for reasons of clarity in each case slightly spaced apart from one another. In reality, the metal composite discs 32 are generally positioned without a spacing with respect to one another. Furthermore, it is possible that a spacing is provided between the laminated rotor core 11 and the two metal composite discs 32 that are positioned directly adjacent to the laminated rotor core 11. The first metal discs 33 comprise on their outer periphery a circumferential bevel 35 that extends in the radial direction as far as the slots 31 of the short-circuit rings 3.

By virtue of the identical hatchings of the elements that represent the rotor bars 2 or rather the first metal discs 33 in FIGS. 1, 2 and 3, it is to be clarified that the rotor bars 2 and the first metal discs 33 are preferably embodied from identical or similar materials. It is particularly preferred that the rotor bars 2 and the first metal discs 33 are embodied from aluminum or an aluminum alloy. As illustrated in FIG. 1, in this case the thickness s₁ of the first metal discs 33 is at least 60% of the total thickness s of the metal composite disc 32. In the case of an alternative embodiment, the rotor bars 2 and the first metal discs 33 can be embodied from copper or a copper alloy.

The rotor bars 21 are bonded, preferably welded, to the first metal discs 33 in the region of the slots 31. This is further explained in connection with FIG. 2.

FIG. 2 illustrates an enlarged section from FIG. 1 in the region of the connection between a rotor bar 2 and the first metal discs 33 of a short-circuit ring. A bonded connection 36 is produced in each case in the region of the slots 31 between the first metal discs 33 and the end region 21 of the rotor bar 2, illustrated in this case in a shortened manner. In the case of a solder connection, the connection 36 can be a solder material that fills a solder gap. In the case of a weld connection, the connection 36 can be formed by means of a molten material of the mutually connected partners or by means of a weld filler material. The two metal discs 34 and the rotor bar 2 are not bonded together, which is illustrated in FIG. 2 in each case by means of a gap between these components.

FIG. 3 illustrates an enlarged section of a further embodiment of a squirrel-cage rotor in accordance with the invention 1 in the region of the connection between a rotor bar 2 and a short-circuit ring 3. In the case of this embodiment, the short-circuit ring 3 comprises two metal composite discs 32 that are arranged in a mirror-inverted manner with respect to one another and comprise in each case a first metal disc 33 and a second metal disc 34, and also metal composite discs 321 that are positioned between said metal composite discs and comprise two first metal discs 33 and a second metal disc 34 that is arranged between two said first metal discs. In each case, a bonded connection 36 is provided in the region of the slots 31 between the first metal discs 33 of the metal composite discs 32 and 321 and the end region 21 of the rotor bar 2, illustrated in this case in a shortened manner. Although the outlay for producing metal composite discs 321 that comprise more than two metal discs 33, 34 is greater than when producing straightforward bi-metal discs, the outlay involved in assembling the short-circuit ring 3 is considerably reduced as a result of using this type of multi-layer metal composite discs 321. The embodiment in accordance with FIG. 3 can be modified to the extent that more than one metal composite disc 321 is used, said one metal composite disc comprising two first metal discs 33 and a second metal disc 34 that is arranged between the two first metal discs 33.

LIST OF REFERENCE NUMERALS

-   1 Squirrel-cage rotor -   11 Laminated rotor core -   12 Groove -   2 Rotor bar -   21 End region -   3 Short-circuit ring -   31 Slot -   32 Metal composite disc -   321 Metal composite disc -   33 First metal disc -   34 Second metal disc -   35 Bevel -   36 Connection -   4 Bore hole -   A Axis -   s Thickness of a metal composite disc -   s₁ Thickness of the first metal disc 

1. Squirrel-cage rotor for an asynchronous machine, said squirrel-cage rotor having at least one laminated rotor core that comprises a plurality of grooves and said squirrel-cage rotor having at least one rotor cage comprising electrically conductive rotor bars that are embedded in the grooves of the laminated rotor core in such a manner that the rotor bars comprise at their two end regions an overlap beyond the laminated rotor core, and said rotor cage comprising short-circuit rings that are attached at the end face to the laminated rotor core and comprise a plurality of slots that are arranged in the region of their outer periphery and the end regions of the rotor bars protrude into said slots, characterized in that the short-circuit rings comprise in each case at least two metal composite discs that comprise at least a first metal disc and a second metal disc that is connected in a planar manner to said first metal disc and is embodied from a different material thereto, that adjacent metal composite discs are arranged at least in part in such a manner that the first metal discs are facing one another and that the rotor bars are bonded to the first metal discs in the region of the slots.
 2. Squirrel-cage rotor according to claim 1, characterized in that the rotor bars are embodied at least in part from a material that can be easily welded to the material of the first metal disc.
 3. Squirrel-cage rotor according to claim 2, characterized in that the rotor bars are embodied at least in part from a material whose base material is identical to the base material of the first metal discs.
 4. Squirrel-cage rotor according to claim 1, characterized in that the first and second metal discs are connected one to the other in a planar manner by means of a plating process.
 5. Squirrel-cage rotor according to claim 1, characterized in that the first metal discs comprise on their outer periphery at least one bevel.
 6. Squirrel-cage rotor according to claim 1, characterized in that the first metal discs are embodied from aluminum or an aluminum alloy.
 7. Squirrel-cage rotor according to claim 6, characterized in that the thickness s₁ of the first metal discs is at least 60% of the thickness s of the metal composite discs.
 8. Squirrel-cage rotor according to claim 1, characterized in that the first metal discs are embodied from copper or a copper alloy. 